(1) Field of the Invention
The present invention relates in general to automated manufacturing of integrated circuit semiconductor devices and more particularly to an automated system where each wafer is handled as a single unit, as contrasted to the more conventional batch processing.
(2) Description of the Prior Art
In the manufacture of semiconductor devices, a circular monocrystalline semiconductor wafer, most typically formed of monocrystalline silicon, is subjected to a large number of processes steps. These process steps include oxidation of the surface to form silicon dioxide insulating layers, deposition of polycrystalline silicon and/or metallic layers, diffusion and/or ion implantation of dopants into selected areas, lithography/masking/etching operations, etching of the various layers mentioned above, heat treating and other steps that are well known to those skilled in the art. A multitude of extremely small and complex electrical circuits are thus formed on the semiconductor wafer through these process steps. As the technology has progressed, the wafers have been made larger and the feature size of the elements of the circuitry on the wafer""s surface have been greatly decreased. This progress has also lead to increasingly faster circuits.
As the size of the circuitry has decreased, airborne contamination becomes responsible for a serious yield problem. Since the integrated circuitry formed upon the silicon wafer is extremely small with feature size on the order of micrometers or submicrometers, it only takes a very small sized particle to either short circuit or cause an open in the formed circuitry. Also, such a particle can block processing chemicals from reaching every portion of the circuitry on the wafer during critical processing steps. Some contamination particles can cause incomplete etching in spaces between lines, thus leading to an unwanted electrical bridge. In addition to such physical defects, other contamination particles may cause electrical failure due to induced ionization or trapping centers in gate dielectric layers.
The main sources of particulate contamination are manufacturing line workers, equipment, and chemicals. Particules given off by workers in the area are transmitted through the environment, and through physical contact or migration onto the wafer surfaces. People, by shedding of skin flakes, for example, are a significant source of particles that are easily ionized and cause defects. It has been found that as many as 6000 particles per minute are emitted into and adjacent a cubic foot of space by a fully suited operator.
An early effort to overcome the contamination problem was to process semiconductor devices in clean rooms with HEPA of ULPA recirculating air systems with suited operators. This procedure is quite expensive and not always effective, particularly in the present era of submicrometer feature size. Although clean room garments reduce particle emissions they do not fully contain the emissions. Also, it is inconvenient and uncomfortable to the operators to remain fully suited at their work throughout the entire work shift.
Movement of semiconductor wafers through the fabrication system for integrated semiconductor devices have long used a cassette system to handle wafers. The wafers are carried in cassettes from processing machine to processing machine. There are many wafers in each cassette. The disadvantage of the cassette system is that the wafers are batch processed, since the cassette is designed to hold many wafers. The cycle time for each wafers then becomes long. This adds to the cost, since a greater inventory is tied up for a longer time. Also, the response time to meet varying customer requirements is long. In addition, the friction between the wafer and the cassette can create particles when the wafers are loaded and unloaded. This contamination occurs in the clean environment and remains there. Still further, the batch transportation of wafers in a cassette or carrier opens the entire batch of wafers to damage from shock loads.
There is a pressing need for a fully automated semiconductor manufacturing system where single wafers are moved between processing stations without exposure to particle laddened air. U.S. Pat. No. 4,540,326 discloses a system for transporting wafers between processing stations where a clean environment is maintained. However, the wafers are loaded and unloaded into a cassette mounted on a cart. This system, however, is a batch operation with the aforedescribed disadvantages. U.S. Pat. No. 3,845,286 describes a wafer processing system wherein single wafers are transported to various processing stations with a transport mechanism. While the broad concept of individual wafer processing is disclosed, the problems concerning contamination are not addressed. U.S. Pat. No. 5,399,531 discloses and claims a manufacturing system for processing individual SC wafers which includes plurality of enclosed processing stations, a tunnel that communicates with the processing stations, a means to move wafers between the stations, and a interface mechanism that moves the wafers from the tunnel to the station.
It should be pointed out that current wafer transport systems occupy large areas of clean room which increases wafer manufacturing cost significantly. One of the key features of this invention is to build the wafer transport and wafer storage area on the top of processing apparatus. By doing so, the clean room area will be used much more effectively.
It is an object of the present invention to provide an improved IC semiconductor manufacturing system that has an improved arrangement of the elements thereof.
Another object to the present invention is to provide an improved manufacturing system where there is better access to the process stations for servicing.
Another object of the present invention is to provide an improved manufacturing system where clean room space will be utilized more effectively by locating the wafer transport system on the top of the processing equipment.
Yet another object of the present invention is to provide an improved manufacturing system that provides a better arrangement of the wafer delivery system.
In accordance with the above objects, there is provided an improved manufacturing system for individually processing semiconductor wafers which includes, a plurality of processing stations, each having an enclosure that is capable of maintaining a controlled clean environment with at least one processing apparatus contained within the enclosure, and a sealed transport tunnel adapted to maintain a controlled clean environment within, with the tunnel located directly above the plurality of processing stations. Interconnection chambers that are adapted to maintain a clean environment within are joined to the tunnel and to the respective enclosures. Interface mechanisms to move wafers are provided in each chamber to move wafers between the tunnel and the processing apparatus in the enclosures.